Insulation for electric conductors.



PATENTED APR. 18, 1905.

L. E. BABRINGBR' INSULATION FOR ELECTRIC OONDUGTORS.

APPLICATION FILED JAN. 30, 1905.

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Witnesses.

UNITED STATES Iatenteo; April 18, 1905.

PATENT OFFICE.

LAVRENOE E. BARRINGER, OF SOHENEOTAIDY, NPHV YORK, ASSIGNOR TO GENERAL ELEO"RIO COMPANY, A CORPORATION OF NEW YORK.

INSULATION FOR ELECTRIC CONDUGTORS.

SPECIFICATION forming part of Letters Patent No. 787,820, dated April 18, 1905.

Application filed January 30,1905. Serial No. 243,197. i

To all who/7i, it Herr/y concern.-

Be it known that l, Lawnnuon E. EARRIN- enu, a citizen of the United States, residing at Schenectady, county of Schenectady, State 5 of New York, have invented certain new and useful Improvements inlnsulation for Electrio Conductors. of which the following is a specification.

The present invention relates to the insula- I tion of electrical conductors, and is especially applicable under circumstances in which the conductor is subjected to a high degree of heat produced by the passage of current through it, as is common in electric heating devices 5 and the like.

The principal object of the invention is to improve the quality of such devices, while at the same time maintaining a low cost of production.

In the ordinary service which electric heating devices must withstand it often happens that the resistance-conductor is left with full current passing through it while the device is not working, as occurs, for example, when an electric water-heater is allowed to boil dry.

This has the effect of greatly increasing'the heat of the conductor and its insulation. To meet this condition, it therefore becomes absolutely necessary, in order to obtain a mar- 3 ketable and satisfactory device, to provide an insulation for the conductor which will retain its good insulating properties at this high temperature as well as at lower temperatures. It has been proposed heretofore in devices of this sort to provide a coat of enamel as the insulation between the conductor and its support; but I have found that when the enamel is heated to the ncighhorhoodof a dull-red heat, as may readily occur under the circum- 4 stances above indicated, it loses in part its insulating properties and becomes slightly conducting. It is also true that under like circumstances the enamel may cease to act as a spacer between the conductor and its support and by reason of its more or less fluid condition permit the conductor to settle by its own weight through the enamel into contact with the supporting metal plate, and thus become wholly or in part short-circuited, thereby destroying the further usefulness of the device. 5

1n the present invention enamel is not used as the insulating substance, but as a binder for holding a more refractory and better insulating material in place. For this purpose I employ some granular substance, such as crushed or ground quartza'ock, calcined porcelain, calcined lire-clay, magnesia, alumina, mica, lava, or the like. Obviously these particles may vary considerably in size, but in common practice are about half the size of rice-grains or smaller.

In applying the insulation the surface to be insulated, which is ordinarily a metal surface, is first coated with a layer of enamel in powdered form and fired as is usual in enameling 5 metal ware. The enamel coating when cool is then covered with a layer of the insulating grains or particles and the enamel is again fused, thereby allowing the particles to adhere to or settle into the enamel, which when 7 cool hardens and holds the particles firmly in place. The granular particles are usually applied in quantity, so as to completely cover the enameled surface, and when the enamel has hardened the superfluous grains are removed. In this way the entire surface of the enamel is covered with the adhering insulating particles.

The relative dimensions of the enamel coating and the insulating particles may vary considerably. For instance, the thickness of the layers of particles that is, the effective thickness of the individual particles may be greater or less than the thickness of the euamcl coating. .Vhen greater, the insulating 5 particles will extend beyond the outer surface of the enamel even when in contact with the supporting-plate and will supportthe eonductor so as to keep it away, not only from the supporting-plate, but even from the en- 9 amel itself. In such cases there can be no leakage between the conductor and the supporting-plate, even when the enamel becomes fluid. On the other hand, the thickness of the particles may be less than that of the enamel coating under circumstances where this leakage is ofno importance, for in any event the insulating particles will serve as a spacer between the supporting-plate and the conductor whatever the condition of the enamel.

Although the invention is capable of general ap iilication, as before indicated, it is especially valuable in the construction of electrically-heated cooking devices, and l have therefore chosen to illustrate it in that conneetion.

In the accompanying drawings, Figure 1 is a vertical section of a frying-pan having its conductor insulated in accordance with the present invention, the plane of section being indicated by the line 1 1 in Fig. 2. Fig. 2 is a plan of the same with-the top plate removed; and Figs-3 and 4 are detail yiews, on an' enlarged scale, showing portions of the conductor together with the adjacent insulation.

The pan itself constitutes no part of my invention, but is illustrated and described herein merely for the purpose of showing a concrete application of the invention.

Referring in detail to the drawings, 10 designates the top plate of the pan, and 11 the body or casing to which it is secured. The casing is provided with three legs 12 and a central aperture for the passage of a bolt 13, by which the main parts of the pan are held together. This bolt screws into a boss 1 1 on the under side of the plate 10 and extends down through and beyond the aperture in the bottom of the casing, where it is provided with a retaining-nut 15, which forces the easing upward into firm engagement with the plate 10.

The electric heating unit is located within the casing 11 and in close relation to the under side of the plate 10. This unit takes the form of a flat spiral formed out of a closely-coiled electric conductor 16, located within a flanged disk or tray 17, also provided with a central aperture which is threaded over the central retaining-bolt 13. The flange of the disk 17 is held in firm engagement with the under side of the top plate 10 by a nut 18 on the bolt 13. The ends of the conductor 16 are connected to binding-posts 19 20, which extend through and are suitably insulated from the disk 17 and are connected, respectively, with other binding-posts, 21 22, by suitable cond uctors 23 2 1, insulated with non-conducting beads 25. The binding-posts 21 22 extend down through and are suitably insulated from the bottom of the casing 11. The lowerends of these posts constitute terminals to which supply-leads may be connected when it is desired to place thedevice in service. ith this organization it now becomes necessary to insulate the adjacent turns of the conductor 16 from each other and from the supporting-disk 17 and the plate 10, to which the energy of the current is to be conducted. For the purpose of insulating the adjacent turns of the conductor mica strips 26 may be employed. These strips are wound spirally around with the helical conductor when it is set in place on the supporting-disk 17. \Vith the mica. strips 26 thus vertically arranged none of the heat has to pass through them on its way to the plate 10. It has been found that where the heat has to pass transversely through mica sheets they soon deteriorate, due to the ready cleavage of the mineral. For this reason it is not practical to insulate the conductor 16 from the plate 10 with mica. Under such circumstances insulation applied according to the present invention is particularly desirable.

1n the drawings, 27 denotes the coating of enamel, and 28 the granular particles of such insulation. In the present instance the entire under surface of the plate 10 and the upper surface of the disk 17, except the flanges, are provided with this insulation. Obviously the insulation must be applied before the parts of the pan are assembled. As previously stated, this is done by enameling these surfaces in the usual way, then applying a quantity of the granular refractory insulating particles to the enameled surfaces, reheati ng the enamel, so that the particles may adhere thereto, and, finally, allowing the enamel to cool and removing the surplus granular material. The enamel serves to bind the particles together and to the supports 10 and 17. The electrical conductor 16 rests directly upon the layer of particles 28 and out of mechanical or electrical contact with the enamel coating 27.

The enamel which I employ may be a silicate, a borosilicate, or a borate in fact, any enamel which may be used with the material of the support to which it is to be affixed, and in ordinary practice it will have a fusing-point ranging between 625 and 1,100 centigrade.

The insulating particles, as previously indicated, may be composed of a variety of substances; but it is an essential requisite of the material that it be a non-conductor of electricity and that it have a fusing-point above that of the enamel. Crushed quartz-rock is the preferred material for this purpose be cause it is a non-conductor at'all temperatures and because of its high fusing-point about 1,800 centigrade-the temperature of 1,800" centigrade not being obtainable with ordinary means, but requiring the oxyhydrogen flame or the electric furnace to accomplish the thorough fusion of the quartz. By the use of particles composed of any of these refractory materials a very etficient insulation is provided. Due-to their high fusing-point the particles will not fuse into the enamel, even though it be heated to a red heat. The insulating properties are also good throughout the range of temperatures at which the device will be used, and, furthermore, when the insulation is used in an electric heating or cooking device the heat of the conductor will be readily cond ucted away from it by the rough surface which the projecting ends of the particles produce, a rough surface more readily absorbing the heat than a smooth enamel surface. It has been found by actual test that there is absolutely no leakage of current between the conductor and its metal support when insulated in this way with particles of sufficient size to hold the conductor away from the enamel, even when-the insulating mass reaches a dullred heat or about 650 centigrade and the conductor is running at 800 centigrade. Insulation made according to the invention has also been found to be very durable and is so firmly attached to its supporting-surface that it can only be detached by a sharp blow of a hammer or similar instrument. Obviously, too, unequal expansion between the conductor and the insulation may take place without injury, since the conductor is free to ride over the surface of theinsulating particles, thus relieving all the parts of injurious strain such as exists where the conductor is partly or wholly embedded in the enamel.

\Vhat I claim as new, and desire to secure by Letters Patent of the United States, is

1. The combination, with a support, of an insulation thereon comprising a coating of a fusible adhesive substance, and particles of an insulating material fusible only at a higher temperature than said adhesive substance embedded in said adhesive coating and projecting beyond the outersurface of the same.

2. The combination, with a support, of an insulation thereon comprising a coating of enamel, and particles of relatively refractory insulating material embedded in said enamel and projecting beyond the outer surface of the same.

3. The combination, with a support, of an insulation thereon comprising a coating of a low-fusing adhesive substance, and particles of quartz embedded in said adhesive coating and projecting beyond the outer surface of the same.

1. The combination, with a support, of an insulation thereon comprising a coating of enameLand particles of crushed quartz embedded in said enamel and projecting beyond the outer surface of the same.

5. The combination of an electrical conductor, a support therefor, and insulation between said conductor and support comprising a layer of insulating particles held together by a coating of adhesive material having a thickness less than the thickness of the layer of particles.

6. The combination of an electrical eonductor, a support therefor, and insulation between said conductor and support comprising a layer of insulating particles having a high fusing-point and a binder for said particles having a thickness less than the thickness of said layer of particles and having a lower fusing-point.

7. The combination of an electrical conductor, a support therefor, and insulation between said conductor and support comprising a layer of crushed quartz particles held together by a coating of adhesive material having a thickness less than the thickness of the layer of particles.

8. The combination of an electrical conductor, a support therefor, and insulation between said conductor and support comprising a layer of insulating particles held together by a coating of enamel having a thickness less than the thickness of the layer of particles.

9. The combination of an electrical conductor, a support therefor, and insulation between said conductor and support comprising a layer of crushed quartz particles held together by a coating of enamel having a thickness less than the thickness of the layer of particles.

10. The combination with a support, of an insulation thereon comprising a layer of insulating particles having a high fusing-point, and a non-earbonizable binder for said particles having a lower fusing-point.

11. The combination with a support, of an insulation thereon comprising a layer of insulating particles having a high fusing-point, and an incombustible binder for said particles having a lower fusing-point.

12. The combination With a support, of an insulation thereon comprising a coating of enamel, and particles of insulating material embedded in said enamel.

13. The combination with a support, of an insulation thereon comprising a coating of a low-fusing adhesive substance, and particles of crushed quartz embedded therein.

1 1. The combination with a support, of an insulation thereon comprising a coating of enamel,and particles of quartz embedded therein.

15. An electrical heater comprising a resistance-wire supported between two metal bodies and insulated by a vitreous coating and an adhesive layer of insulating fragments infusible at a red heat of the wire.

16. The combination of a resistance-wire fusing above a red heat, a support therefor covered with vitreous insulation, and a spacer between the two consisting of a material which is neither softened nor decomposed at a redheat temperature of the conductor, said material being affixed to the vitreous insulation when the latter is soft.

In witness whereof I have hereunto set my hand this 27th day of January, 1905.

LAIVRENCE E. BARRINGER.

WVitnesses:

BENJAMIN B. HULL, HELEN Onronn. 

